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1 .nr PS 11
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2 .nr VS 13
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3
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4 .de CW
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5 .nr PQ \\n(.f
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6 .if t \{\
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7 . ft CW
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meillo@48
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8 . if !^\\$1^^ \&\\$1\f\\n(PQ\\$2
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9 .\}
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10 .if n \{\
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meillo@48
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11 . ie ^\\$1^^ .ul 999
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12 . el .ul 1
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13 . if \\n(.$=1 \&\\$1
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14 . if \\n(.$>1 \&\\$1\c
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15 . if \\n(.$>1 \&\\$2
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16 .\}
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meillo@0
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17 ..
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18
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meillo@0
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19 .ds [. \ [
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20 .ds .] ]
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meillo@42
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21
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22 .de H
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meillo@48
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23 .if '\\$1'1' \{\
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24 . sp 2v
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25 . nr PS +2
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26 . NH \\$1
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27 \\$2
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28 . nr PS -2
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29 . LP
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30 . XS
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31 . sp .5v
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32 . B
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33 \\*(SN \\$2
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34 . XE
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meillo@48
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35 .\}
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meillo@48
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36 .if '\\$1'2' \{\
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meillo@48
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37 . NH \\$1
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38 \\$2
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meillo@48
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39 . LP
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meillo@48
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40 . XS
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41 \\*(SN \\$2
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42 . XE
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43 .\}
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44 ..
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45
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46 .am QP
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47 .ps -1
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48 ..
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49
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50 .am DS
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51 .CW
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52 .ps -1
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53 ..
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54
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meillo@1
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55 .\"----------------------------------------
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56
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meillo@0
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57 .TL
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58 .ps +4
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meillo@6
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59 Why the Unix Philosophy still matters
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60 .AU
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meillo@0
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61 markus schnalke <meillo@marmaro.de>
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62 .AB
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63 .ti \n(.iu
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meillo@39
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64 This paper explains the importance of the Unix Philosophy for software design.
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65 Today, few software designers are aware of these concepts,
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66 and thus a lot of modern software is more limited than necessary
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67 and makes less use of software leverage than possible.
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meillo@38
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68 Knowing and following the guidelines of the Unix Philosophy makes software more valuable.
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meillo@0
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69 .AE
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70
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meillo@2
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71 .FS
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72 .ps -1
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73 This paper was prepared for the ``Software Analysis'' seminar at University Ulm.
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74 Mentor was professor Franz Schweiggert.
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75 Handed in on 2010-04-12.
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meillo@39
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76 You may retrieve this document from
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77 .CW \s-1http://marmaro.de/docs \ .
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meillo@2
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78 .FE
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79
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80 .H 1 Introduction
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81 .LP
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82 The Unix Philosophy is the essence of how the Unix operating system,
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meillo@40
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83 especially its toolchest, was designed.
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84 It is no limited set of fixed rules,
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85 but a loose set of guidelines which tell how to write software that
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meillo@40
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86 suites well into Unix.
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meillo@40
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87 Actually, the Unix Philosophy describes what is common to typical Unix software.
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meillo@40
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88 The Wikipedia has an accurate definition:
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meillo@40
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89 .[
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90 wikipedia
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91 unix philosophy
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meillo@40
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92 .]
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93 .QP
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94 The \fIUnix philosophy\fP is a set of cultural norms and philosophical
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95 approaches to developing software based on the experience of leading
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96 developers of the Unix operating system.
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meillo@1
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97 .PP
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98 As there is no single definition of the Unix Philosophy,
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meillo@40
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99 several people have stated their view on what it comprises.
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meillo@1
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100 Best known are:
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meillo@1
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101 .IP \(bu
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meillo@1
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102 Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
|
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meillo@1
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103 .[
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meillo@44
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104 mahoney
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meillo@44
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105 oral history
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meillo@1
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106 .]
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meillo@1
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107 .IP \(bu
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meillo@1
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108 Mike Gancarz' book ``The UNIX Philosophy''.
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meillo@1
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109 .[
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meillo@44
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110 gancarz
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111 unix philosophy
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meillo@1
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112 .]
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meillo@1
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113 .IP \(bu
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meillo@1
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114 Eric S. Raymond's book ``The Art of UNIX Programming''.
|
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meillo@1
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115 .[
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meillo@44
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116 raymond
|
|
meillo@44
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117 art of unix programming
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meillo@1
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118 .]
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meillo@0
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119 .LP
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meillo@1
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120 These different views on the Unix Philosophy have much in common.
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meillo@40
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121 Especially, the main concepts are similar in all of them.
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meillo@40
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122 McIlroy's definition can surely be called the core of the Unix Philosophy,
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meillo@40
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123 but the fundamental idea behind it all, is ``small is beautiful''.
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meillo@40
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124
|
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meillo@40
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125 .PP
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meillo@45
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126 The Unix Philosophy explains how to design good software for Unix.
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meillo@45
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127 Many concepts described here, base on facilities of Unix.
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meillo@40
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128 Other operating systems may not offer such facilities,
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meillo@41
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129 hence it may not be possible to design software in the way of the
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meillo@41
|
130 Unix Philosophy for them.
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meillo@40
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131 .PP
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meillo@41
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132 The Unix Philosophy has an idea of how the process of software development
|
|
meillo@41
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133 should look like, but large parts of the philosophy are quite independent
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meillo@45
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134 from a concrete development process.
|
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meillo@41
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135 However, one will soon recognize that some development processes work well
|
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meillo@41
|
136 with the ideas of the Unix Philosophy and support them, while others are
|
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meillo@41
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137 at cross-purposes.
|
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meillo@45
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138 Kent Beck's books about Extreme Programming are valuable supplemental
|
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meillo@45
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139 resources on this topic.
|
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meillo@1
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140 .PP
|
|
meillo@41
|
141 The question of how to actually write code and how the code should looks
|
|
meillo@45
|
142 like in detail, are out of focus here.
|
|
meillo@41
|
143 ``The Practice of Programming'' by Kernighan and Pike,
|
|
meillo@41
|
144 .[
|
|
meillo@44
|
145 kernighan pike
|
|
meillo@44
|
146 practice of programming
|
|
meillo@41
|
147 .]
|
|
meillo@41
|
148 is a good book that covers this topic.
|
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meillo@41
|
149 Its point of view matches to the one of this paper.
|
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meillo@0
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150
|
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meillo@48
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151 .H 1 "Importance of software design in general
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meillo@0
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152 .LP
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meillo@40
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153 Software design is the planning of how the internal structure
|
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meillo@40
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154 and external interfaces of a software should look like.
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meillo@39
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155 It has nothing to do with visual appearance.
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meillo@39
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156 If we take a program as a car, then its color is of no matter.
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meillo@39
|
157 Its design would be the car's size, its shape, the locations of doors,
|
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meillo@45
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158 the passenger/space ratio, the available controls and instruments,
|
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meillo@45
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159 and so forth.
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meillo@39
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160 .PP
|
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meillo@39
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161 Why should software get designed at all?
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meillo@6
|
162 It is general knowledge, that even a bad plan is better than no plan.
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meillo@39
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163 Not designing software means programming without plan.
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meillo@39
|
164 This will pretty sure lead to horrible results.
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meillo@45
|
165 Software that is horrible to use and horrible to maintain.
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meillo@39
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166 These two aspects are the visible ones.
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meillo@45
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167 Often invisible though, are the wasted possible gains.
|
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meillo@39
|
168 Good software design can make these gains available.
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meillo@2
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169 .PP
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meillo@39
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170 A software's design deals with quality properties.
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meillo@39
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171 Good design leads to good quality, and quality is important.
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meillo@39
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172 Any car may be able to drive from A to B,
|
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meillo@39
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173 but it depends on the car's properties whether it is a good choice
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meillo@39
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174 for passenger transport or not.
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meillo@39
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175 It depends on its properties if it is a good choice
|
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meillo@39
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176 for a rough mountain area.
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meillo@39
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177 And it depends on its properties if the ride will be fun.
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meillo@39
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178
|
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meillo@2
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179 .PP
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meillo@39
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180 Requirements for a software are twofold:
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meillo@39
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181 functional and non-functional.
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meillo@39
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182 .IP \(bu
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meillo@39
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183 Functional requirements define directly the software's functions.
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meillo@39
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184 They are the reason why software gets written.
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meillo@39
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185 Someone has a problem and needs a tool to solve it.
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meillo@39
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186 Being able to solve the problem is the main functional goal.
|
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meillo@39
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187 It is the driving force behind all programming effort.
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meillo@39
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188 Functional requirements are easier to define and to verify.
|
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meillo@39
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189 .IP \(bu
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meillo@45
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190 Non-functional requirements are called \fIquality\fP requirements, too.
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meillo@39
|
191 The quality of a software are the properties that are not directly related to
|
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meillo@39
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192 the software's basic functions.
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meillo@45
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193 Tools of bad quality often do solve the problems they were written for,
|
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meillo@39
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194 but introduce problems and difficulties for usage and development, later on.
|
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195 Quality aspects are often overlooked at first sight,
|
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meillo@45
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196 and are often difficult to define clearly and to verify.
|
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meillo@2
|
197 .PP
|
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meillo@45
|
198 Quality is hardly interesting when the software gets built initially,
|
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meillo@45
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199 but it has a high impact on usability and maintenance of the software, later.
|
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meillo@45
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200 A short-sighted might see in developing a software, mainly building something up.
|
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meillo@39
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201 But experience shows, that building the software the first time is
|
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meillo@39
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202 only a small amount of the overall work.
|
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meillo@45
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203 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en
|
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meillo@6
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204 does soon take over the major part of the time spent on a software.
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meillo@45
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205 And of course, the time spent actually using the software.
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meillo@6
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206 These processes are highly influenced by the software's quality.
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meillo@39
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207 Thus, quality must not be neglected.
|
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meillo@45
|
208 However, the problem with quality is that you hardly ``stumble over''
|
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meillo@39
|
209 bad quality during the first build,
|
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meillo@45
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210 although this is the time when you should care about good quality most.
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meillo@6
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211 .PP
|
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meillo@45
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212 Software design has little to do with the basic function of a software \(en
|
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meillo@39
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213 this requirement will get satisfied anyway.
|
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meillo@39
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214 Software design is more about quality aspects of the software.
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meillo@39
|
215 Good design leads to good quality, bad design to bad quality.
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meillo@6
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216 The primary functions of the software will be affected modestly by bad quality,
|
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meillo@39
|
217 but good quality can provide a lot of additional gain,
|
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meillo@6
|
218 even at places where one never expected it.
|
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meillo@6
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219 .PP
|
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meillo@45
|
220 The ISO/IEC\|9126-1 standard, part\|1,
|
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meillo@6
|
221 .[
|
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meillo@44
|
222 iso product quality
|
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meillo@6
|
223 .]
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meillo@6
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224 defines the quality model as consisting out of:
|
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meillo@6
|
225 .IP \(bu
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meillo@6
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226 .I Functionality
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meillo@6
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227 (suitability, accuracy, inter\%operability, security)
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meillo@6
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228 .IP \(bu
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meillo@6
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229 .I Reliability
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meillo@6
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230 (maturity, fault tolerance, recoverability)
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meillo@6
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231 .IP \(bu
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meillo@6
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232 .I Usability
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meillo@6
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233 (understandability, learnability, operability, attractiveness)
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meillo@6
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234 .IP \(bu
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meillo@6
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235 .I Efficiency
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meillo@9
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236 (time behavior, resource utilization)
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meillo@6
|
237 .IP \(bu
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meillo@6
|
238 .I Maintainability
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meillo@23
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239 (analyzability, changeability, stability, testability)
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meillo@6
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240 .IP \(bu
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meillo@6
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241 .I Portability
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meillo@6
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242 (adaptability, installability, co-existence, replaceability)
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meillo@6
|
243 .LP
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meillo@39
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244 Good design can improve these properties of a software,
|
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meillo@45
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245 bad designed software likely suffers in these points.
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meillo@7
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246 .PP
|
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meillo@7
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247 One further goal of software design is consistency.
|
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meillo@7
|
248 Consistency eases understanding, working on, and using things.
|
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meillo@39
|
249 Consistent internal structure and consistent interfaces to the outside
|
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meillo@39
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250 can be provided by good design.
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meillo@7
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251 .PP
|
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meillo@39
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252 Software should be well designed because good design avoids many
|
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meillo@45
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253 problems during a software's lifetime.
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meillo@39
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254 And software should be well designed because good design can offer
|
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meillo@39
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255 much additional gain.
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meillo@39
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256 Indeed, much effort should be spent into good design to make software more valuable.
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meillo@39
|
257 The Unix Philosophy shows a way of how to design software well.
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meillo@7
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258 It offers guidelines to achieve good quality and high gain for the effort spent.
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meillo@0
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259
|
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meillo@0
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260
|
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meillo@48
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261 .H 1 "The Unix Philosophy
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meillo@4
|
262 .LP
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meillo@4
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263 The origins of the Unix Philosophy were already introduced.
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meillo@8
|
264 This chapter explains the philosophy, oriented on Gancarz,
|
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meillo@8
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265 and shows concrete examples of its application.
|
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meillo@5
|
266
|
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meillo@48
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267 .H 2 Pipes
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meillo@4
|
268 .LP
|
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meillo@4
|
269 Following are some examples to demonstrate how applied Unix Philosophy feels like.
|
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meillo@4
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270 Knowledge of using the Unix shell is assumed.
|
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meillo@4
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271 .PP
|
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meillo@4
|
272 Counting the number of files in the current directory:
|
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meillo@41
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273 .DS
|
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meillo@4
|
274 ls | wc -l
|
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meillo@4
|
275 .DE
|
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meillo@4
|
276 The
|
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meillo@4
|
277 .CW ls
|
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meillo@4
|
278 command lists all files in the current directory, one per line,
|
|
meillo@4
|
279 and
|
|
meillo@4
|
280 .CW "wc -l
|
|
meillo@8
|
281 counts the number of lines.
|
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meillo@4
|
282 .PP
|
|
meillo@8
|
283 Counting the number of files that do not contain ``foo'' in their name:
|
|
meillo@41
|
284 .DS
|
|
meillo@4
|
285 ls | grep -v foo | wc -l
|
|
meillo@4
|
286 .DE
|
|
meillo@4
|
287 Here, the list of files is filtered by
|
|
meillo@4
|
288 .CW grep
|
|
meillo@45
|
289 to remove all lines that contain ``foo''.
|
|
meillo@45
|
290 The rest equals the previous example.
|
|
meillo@4
|
291 .PP
|
|
meillo@4
|
292 Finding the five largest entries in the current directory.
|
|
meillo@41
|
293 .DS
|
|
meillo@4
|
294 du -s * | sort -nr | sed 5q
|
|
meillo@4
|
295 .DE
|
|
meillo@4
|
296 .CW "du -s *
|
|
meillo@45
|
297 returns the recursively summed sizes of all files in the current directory
|
|
meillo@8
|
298 \(en no matter if they are regular files or directories.
|
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meillo@4
|
299 .CW "sort -nr
|
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meillo@45
|
300 sorts the list numerically in reverse order (descending).
|
|
meillo@4
|
301 Finally,
|
|
meillo@4
|
302 .CW "sed 5q
|
|
meillo@4
|
303 quits after it has printed the fifth line.
|
|
meillo@4
|
304 .PP
|
|
meillo@4
|
305 The presented command lines are examples of what Unix people would use
|
|
meillo@4
|
306 to get the desired output.
|
|
meillo@4
|
307 There are also other ways to get the same output.
|
|
meillo@4
|
308 It's a user's decision which way to go.
|
|
meillo@14
|
309 .PP
|
|
meillo@8
|
310 The examples show that many tasks on a Unix system
|
|
meillo@4
|
311 are accomplished by combining several small programs.
|
|
meillo@4
|
312 The connection between the single programs is denoted by the pipe operator `|'.
|
|
meillo@4
|
313 .PP
|
|
meillo@4
|
314 Pipes, and their extensive and easy use, are one of the great
|
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meillo@4
|
315 achievements of the Unix system.
|
|
meillo@4
|
316 Pipes between programs have been possible in earlier operating systems,
|
|
meillo@4
|
317 but it has never been a so central part of the concept.
|
|
meillo@45
|
318 When, in the early seventies, Doug McIlroy introduced pipes into the
|
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meillo@4
|
319 Unix system,
|
|
meillo@4
|
320 ``it was this concept and notation for linking several programs together
|
|
meillo@4
|
321 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
|
|
meillo@4
|
322 .[
|
|
meillo@44
|
323 aughenbaugh
|
|
meillo@44
|
324 unix oral history
|
|
meillo@45
|
325 .]
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|
meillo@4
|
326 .PP
|
|
meillo@4
|
327 Being able to specify pipelines in an easy way is,
|
|
meillo@4
|
328 however, not enough by itself.
|
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meillo@5
|
329 It is only one half.
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meillo@4
|
330 The other is the design of the programs that are used in the pipeline.
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meillo@45
|
331 They need interfaces that allow them to be used in such a way.
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meillo@5
|
332
|
|
meillo@48
|
333 .H 2 "Interface design
|
|
meillo@5
|
334 .LP
|
|
meillo@11
|
335 Unix is, first of all, simple \(en Everything is a file.
|
|
meillo@5
|
336 Files are sequences of bytes, without any special structure.
|
|
meillo@45
|
337 Programs should be filters, which read a stream of bytes from standard input (stdin)
|
|
meillo@45
|
338 and write a stream of bytes to standard output (stdout).
|
|
meillo@8
|
339 If the files \fIare\fP sequences of bytes,
|
|
meillo@8
|
340 and the programs \fIare\fP filters on byte streams,
|
|
meillo@45
|
341 then there is exactly one data interface.
|
|
meillo@45
|
342 Hence it is possible to combine programs in any desired way.
|
|
meillo@5
|
343 .PP
|
|
meillo@45
|
344 Even a handful of small programs yields a large set of combinations,
|
|
meillo@5
|
345 and thus a large set of different functions.
|
|
meillo@5
|
346 This is leverage!
|
|
meillo@5
|
347 If the programs are orthogonal to each other \(en the best case \(en
|
|
meillo@5
|
348 then the set of different functions is greatest.
|
|
meillo@5
|
349 .PP
|
|
meillo@45
|
350 Programs can also have a separate control interface,
|
|
meillo@11
|
351 besides their data interface.
|
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meillo@11
|
352 The control interface is often called ``user interface'',
|
|
meillo@11
|
353 because it is usually designed to be used by humans.
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meillo@11
|
354 The Unix Philosophy discourages to assume the user to be human.
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meillo@11
|
355 Interactive use of software is slow use of software,
|
|
meillo@11
|
356 because the program waits for user input most of the time.
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|
meillo@45
|
357 Interactive software requires the user to be in front of the computer.
|
|
meillo@11
|
358 Interactive software occupy the user's attention while they are running.
|
|
meillo@11
|
359 .PP
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|
meillo@45
|
360 Now to come back to the idea of combining several small programs,
|
|
meillo@11
|
361 to have a more specific function.
|
|
meillo@11
|
362 If these single tools would all be interactive,
|
|
meillo@11
|
363 how would the user control them?
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|
meillo@45
|
364 It is not only a problem to control several programs at once,
|
|
meillo@45
|
365 if they run at the same time,
|
|
meillo@11
|
366 it also very inefficient to have to control each of the single programs
|
|
meillo@45
|
367 that are intended to act as one large program.
|
|
meillo@11
|
368 Hence, the Unix Philosophy discourages programs to demand interactive use.
|
|
meillo@11
|
369 The behavior of programs should be defined at invocation.
|
|
meillo@45
|
370 This is done by specifying arguments to the program call
|
|
meillo@45
|
371 (command line switches).
|
|
meillo@11
|
372 Gancarz discusses this topic as ``avoid captive user interfaces''.
|
|
meillo@46
|
373 .[ [
|
|
meillo@44
|
374 gancarz unix philosophy
|
|
meillo@46
|
375 .], page 88 ff.]
|
|
meillo@11
|
376 .PP
|
|
meillo@11
|
377 Non-interactive use is, during development, also an advantage for testing.
|
|
meillo@11
|
378 Testing of interactive programs is much more complicated,
|
|
meillo@11
|
379 than testing of non-interactive programs.
|
|
meillo@5
|
380
|
|
meillo@48
|
381 .H 2 "The toolchest approach
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|
meillo@5
|
382 .LP
|
|
meillo@5
|
383 A toolchest is a set of tools.
|
|
meillo@5
|
384 Instead of having one big tool for all tasks, one has many small tools,
|
|
meillo@5
|
385 each for one task.
|
|
meillo@5
|
386 Difficult tasks are solved by combining several of the small, simple tools.
|
|
meillo@5
|
387 .PP
|
|
meillo@11
|
388 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
|
|
meillo@11
|
389 that are filters on byte streams.
|
|
meillo@11
|
390 They are, to a large extend, unrelated in their function.
|
|
meillo@11
|
391 Hence, the Unix toolchest provides a large set of functions
|
|
meillo@11
|
392 that can be accessed by combining the programs in the desired way.
|
|
meillo@11
|
393 .PP
|
|
meillo@11
|
394 There are also advantages for developing small toolchest programs.
|
|
meillo@5
|
395 It is easier and less error-prone to write small programs.
|
|
meillo@5
|
396 It is also easier and less error-prone to write a large set of small programs,
|
|
meillo@5
|
397 than to write one large program with all the functionality included.
|
|
meillo@5
|
398 If the small programs are combinable, then they offer even a larger set
|
|
meillo@5
|
399 of functions than the single large program.
|
|
meillo@45
|
400 Hence, one gets two advantages out of writing small, combinable programs:
|
|
meillo@45
|
401 They are easier to write and they offer a greater set of functions through
|
|
meillo@45
|
402 combination.
|
|
meillo@5
|
403 .PP
|
|
meillo@45
|
404 But there are also two main drawbacks of the toolchest approach.
|
|
meillo@45
|
405 First, one simple, standardized interface has to be sufficient.
|
|
meillo@5
|
406 If one feels the need for more ``logic'' than a stream of bytes,
|
|
meillo@8
|
407 then a different approach might be of need.
|
|
meillo@13
|
408 But it is also possible, that he just can not imagine a design where
|
|
meillo@8
|
409 a stream of bytes is sufficient.
|
|
meillo@8
|
410 By becoming more familiar with the ``Unix style of thinking'',
|
|
meillo@8
|
411 developers will more often and easier find simple designs where
|
|
meillo@8
|
412 a stream of bytes is a sufficient interface.
|
|
meillo@8
|
413 .PP
|
|
meillo@8
|
414 The second drawback of a toolchest affects the users.
|
|
meillo@45
|
415 A toolchest is often more difficult to use.
|
|
meillo@9
|
416 It is necessary to become familiar with each of the tools,
|
|
meillo@5
|
417 to be able to use the right one in a given situation.
|
|
meillo@45
|
418 Additionally, one needs to combine the tools in a senseful way himself.
|
|
meillo@45
|
419 This is like a sharp knife \(en it is a powerful tool in the hand of a
|
|
meillo@45
|
420 master, but of no good value in the hand of an unskilled.
|
|
meillo@45
|
421 However, learning single, small tools of a toolchest is easier than
|
|
meillo@45
|
422 learning a complex tool.
|
|
meillo@45
|
423 And the user will already have a basic understanding of a yet unknown tool,
|
|
meillo@45
|
424 if the tools of a toolchest have a common, consistent style.
|
|
meillo@45
|
425 He will be able to transfer knowledge over from one tool to another.
|
|
meillo@5
|
426 .PP
|
|
meillo@45
|
427 Moreover, the second drawback can be removed to a large extend
|
|
meillo@45
|
428 by adding wrappers around the basic tools.
|
|
meillo@45
|
429 Novice users do not need to learn several tools, if a professional wraps
|
|
meillo@45
|
430 complete command lines into a higher-level script.
|
|
meillo@5
|
431 Note that the wrapper script still calls the small tools;
|
|
meillo@45
|
432 it is just like a skin around them.
|
|
meillo@45
|
433 No complexity is added this way.
|
|
meillo@45
|
434 But new programs can get created out of existing one with very low effort.
|
|
meillo@5
|
435 .PP
|
|
meillo@5
|
436 A wrapper script for finding the five largest entries in the current directory
|
|
meillo@5
|
437 could look like this:
|
|
meillo@41
|
438 .DS
|
|
meillo@5
|
439 #!/bin/sh
|
|
meillo@5
|
440 du -s * | sort -nr | sed 5q
|
|
meillo@5
|
441 .DE
|
|
meillo@45
|
442 The script itself is just a text file that calls the command line,
|
|
meillo@45
|
443 which a professional user would type in directly.
|
|
meillo@45
|
444 It is probably worth to make the program flexible on the number of
|
|
meillo@45
|
445 entries it prints:
|
|
meillo@41
|
446 .DS
|
|
meillo@8
|
447 #!/bin/sh
|
|
meillo@8
|
448 num=5
|
|
meillo@8
|
449 [ $# -eq 1 ] && num="$1"
|
|
meillo@8
|
450 du -sh * | sort -nr | sed "${num}q"
|
|
meillo@8
|
451 .DE
|
|
meillo@8
|
452 This script acts like the one before, when called without an argument.
|
|
meillo@8
|
453 But one can also specify a numerical argument to define the number of lines to print.
|
|
meillo@45
|
454 One can surely imagine even more flexible versions, however,
|
|
meillo@45
|
455 they will still relay on the external programs,
|
|
meillo@45
|
456 which do the actual work.
|
|
meillo@5
|
457
|
|
meillo@48
|
458 .H 2 "A powerful shell
|
|
meillo@8
|
459 .LP
|
|
meillo@45
|
460 The Unix shell provides the possibility to combine small programs into large ones.
|
|
meillo@45
|
461 But a powerful shell is a great feature in other ways, too.
|
|
meillo@45
|
462 For instance by being scriptable.
|
|
meillo@45
|
463 Control statements are build into the shell.
|
|
meillo@45
|
464 The functions, however, are the normal programs of the system.
|
|
meillo@45
|
465 Thus, as the programs are already known,
|
|
meillo@45
|
466 learning to program in the shell becomes easy.
|
|
meillo@8
|
467 Using normal programs as functions in the shell programming language
|
|
meillo@10
|
468 is only possible because they are small and combinable tools in a toolchest style.
|
|
meillo@8
|
469 .PP
|
|
meillo@45
|
470 The Unix shell encourages to write small scripts,
|
|
meillo@45
|
471 by combining existing programs, because it is so easy to do.
|
|
meillo@8
|
472 This is a great step towards automation.
|
|
meillo@8
|
473 It is wonderful if the effort to automate a task equals the effort
|
|
meillo@45
|
474 to do the task a second time by hand.
|
|
meillo@45
|
475 If this holds,
|
|
meillo@45
|
476 then the user will be happy to automate everything he does more than once.
|
|
meillo@8
|
477 .PP
|
|
meillo@8
|
478 Small programs that do one job well, standardized interfaces between them,
|
|
meillo@8
|
479 a mechanism to combine parts to larger parts, and an easy way to automate tasks,
|
|
meillo@8
|
480 this will inevitably produce software leverage.
|
|
meillo@8
|
481 Getting multiple times the benefit of an investment is a great offer.
|
|
meillo@10
|
482 .PP
|
|
meillo@10
|
483 The shell also encourages rapid prototyping.
|
|
meillo@10
|
484 Many well known programs started as quickly hacked shell scripts,
|
|
meillo@10
|
485 and turned into ``real'' programs, written in C, later.
|
|
meillo@45
|
486 Building a prototype first, is a way to avoid the biggest problems
|
|
meillo@10
|
487 in application development.
|
|
meillo@45
|
488 Fred Brooks explains in ``No Silver Bullet'':
|
|
meillo@10
|
489 .[
|
|
meillo@44
|
490 brooks
|
|
meillo@44
|
491 no silver bullet
|
|
meillo@10
|
492 .]
|
|
meillo@10
|
493 .QP
|
|
meillo@10
|
494 The hardest single part of building a software system is deciding precisely what to build.
|
|
meillo@10
|
495 No other part of the conceptual work is so difficult as establishing the detailed
|
|
meillo@10
|
496 technical requirements, [...].
|
|
meillo@10
|
497 No other part of the work so cripples the resulting system if done wrong.
|
|
meillo@10
|
498 No other part is more difficult to rectify later.
|
|
meillo@10
|
499 .PP
|
|
meillo@45
|
500 Writing a prototype is a great method for becoming familiar with the requirements
|
|
meillo@45
|
501 and to run into real problems early.
|
|
meillo@47
|
502 .[ [
|
|
meillo@47
|
503 gancarz
|
|
meillo@47
|
504 unix philosophy
|
|
meillo@47
|
505 .], page 28 f.]
|
|
meillo@45
|
506 .PP
|
|
meillo@45
|
507 Prototyping is often seen as a first step in building a software.
|
|
meillo@10
|
508 This is, of course, good.
|
|
meillo@10
|
509 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
|
|
meillo@10
|
510 After having built the prototype, one might notice, that the prototype is already
|
|
meillo@10
|
511 \fIgood enough\fP.
|
|
meillo@45
|
512 Hence, no reimplementation, in a more sophisticated programming language,
|
|
meillo@45
|
513 might be of need, at least for the moment.
|
|
meillo@23
|
514 Maybe later, it might be necessary to rewrite the software, but not now.
|
|
meillo@45
|
515 By delaying further work, one keeps the flexibility to react on
|
|
meillo@10
|
516 changing requirements.
|
|
meillo@10
|
517 Software parts that are not written will not miss the requirements.
|
|
meillo@10
|
518
|
|
meillo@48
|
519 .H 2 "Worse is better
|
|
meillo@10
|
520 .LP
|
|
meillo@45
|
521 The Unix Philosophy aims for the 90% solution;
|
|
meillo@10
|
522 others call it the ``Worse is better'' approach.
|
|
meillo@47
|
523 Experience from real life projects shows:
|
|
meillo@10
|
524 .PP
|
|
meillo@45
|
525 (1) It is almost never possible to define the
|
|
meillo@10
|
526 requirements completely and correctly the first time.
|
|
meillo@45
|
527 Hence one should not try to; one will fail anyway.
|
|
meillo@45
|
528 .PP
|
|
meillo@45
|
529 (2) Requirements change during time.
|
|
meillo@10
|
530 Hence it is best to delay requirement-based design decisions as long as possible.
|
|
meillo@45
|
531 The software should be small and flexible as long as possible
|
|
meillo@10
|
532 to react on changing requirements.
|
|
meillo@10
|
533 Shell scripts, for example, are more easily adjusted as C programs.
|
|
meillo@45
|
534 .PP
|
|
meillo@45
|
535 (3) Maintenance work is hard work.
|
|
meillo@45
|
536 Hence, one should keep the amount of code as small as possible;
|
|
meillo@10
|
537 it should just fulfill the \fIcurrent\fP requirements.
|
|
meillo@45
|
538 Software parts that will be written in future,
|
|
meillo@45
|
539 do not need maintenance till then.
|
|
meillo@10
|
540 .PP
|
|
meillo@47
|
541 See Brooks' ``The Mythical Man-Month'' for reference.
|
|
meillo@47
|
542 .[ [
|
|
meillo@47
|
543 brooks
|
|
meillo@47
|
544 mythical man-month
|
|
meillo@47
|
545 .], page 115 ff.]
|
|
meillo@47
|
546 .PP
|
|
meillo@10
|
547 Starting with a prototype in a scripting language has several advantages:
|
|
meillo@10
|
548 .IP \(bu
|
|
meillo@10
|
549 As the initial effort is low, one will likely start right away.
|
|
meillo@10
|
550 .IP \(bu
|
|
meillo@10
|
551 As working parts are available soon, the real requirements can get identified soon.
|
|
meillo@10
|
552 .IP \(bu
|
|
meillo@45
|
553 When a software is usable and valuable, it gets used, and thus tested.
|
|
meillo@10
|
554 Hence problems will be found at early stages of the development.
|
|
meillo@10
|
555 .IP \(bu
|
|
meillo@10
|
556 The prototype might be enough for the moment,
|
|
meillo@45
|
557 thus further work on the software can get delayed to a time
|
|
meillo@10
|
558 when one knows better about the requirements and problems,
|
|
meillo@10
|
559 than now.
|
|
meillo@10
|
560 .IP \(bu
|
|
meillo@45
|
561 Implementing now only the parts that are actually needed at the moment,
|
|
meillo@45
|
562 introduces fewer programming and maintenance work.
|
|
meillo@10
|
563 .IP \(bu
|
|
meillo@10
|
564 If the global situation changes so that the software is not needed anymore,
|
|
meillo@10
|
565 then less effort was spent into the project, than it would have be
|
|
meillo@10
|
566 when a different approach had been used.
|
|
meillo@10
|
567
|
|
meillo@48
|
568 .H 2 "Upgrowth and survival of software
|
|
meillo@11
|
569 .LP
|
|
meillo@12
|
570 So far it was talked about \fIwriting\fP or \fIbuilding\fP software.
|
|
meillo@13
|
571 Although these are just verbs, they do imply a specific view on the work process
|
|
meillo@13
|
572 they describe.
|
|
meillo@12
|
573 The better verb, however, is to \fIgrow\fP.
|
|
meillo@12
|
574 Creating software in the sense of the Unix Philosophy is an incremental process.
|
|
meillo@12
|
575 It starts with a first prototype, which evolves as requirements change.
|
|
meillo@12
|
576 A quickly hacked shell script might become a large, sophisticated,
|
|
meillo@13
|
577 compiled program this way.
|
|
meillo@13
|
578 Its lifetime begins with the initial prototype and ends when the software is not used anymore.
|
|
meillo@45
|
579 While being alive it will get extended, rearranged, rebuilt.
|
|
meillo@12
|
580 Growing software matches the view that ``software is never finished. It is only released.''
|
|
meillo@46
|
581 .[ [
|
|
meillo@44
|
582 gancarz
|
|
meillo@44
|
583 unix philosophy
|
|
meillo@46
|
584 .], page 26]
|
|
meillo@12
|
585 .PP
|
|
meillo@13
|
586 Software can be seen as being controlled by evolutionary processes.
|
|
meillo@13
|
587 Successful software is software that is used by many for a long time.
|
|
meillo@12
|
588 This implies that the software is needed, useful, and better than alternatives.
|
|
meillo@12
|
589 Darwin talks about: ``The survival of the fittest.''
|
|
meillo@12
|
590 .[
|
|
meillo@44
|
591 darwin
|
|
meillo@44
|
592 origin of species
|
|
meillo@12
|
593 .]
|
|
meillo@12
|
594 Transferred to software: The most successful software, is the fittest,
|
|
meillo@12
|
595 is the one that survives.
|
|
meillo@13
|
596 (This may be at the level of one creature, or at the level of one species.)
|
|
meillo@13
|
597 The fitness of software is affected mainly by four properties:
|
|
meillo@15
|
598 portability of code, portability of data, range of usability, and reusability of parts.
|
|
meillo@13
|
599 .PP
|
|
meillo@15
|
600 (1)
|
|
meillo@15
|
601 .I "Portability of code
|
|
meillo@15
|
602 means, using high-level programming languages,
|
|
meillo@13
|
603 sticking to the standard,
|
|
meillo@47
|
604 .[ [
|
|
meillo@47
|
605 kernighan pike
|
|
meillo@47
|
606 practice of programming
|
|
meillo@47
|
607 .], chapter\|8]
|
|
meillo@13
|
608 and avoiding optimizations that introduce dependencies on specific hardware.
|
|
meillo@13
|
609 Hardware has a much lower lifetime than software.
|
|
meillo@13
|
610 By chaining software to a specific hardware,
|
|
meillo@13
|
611 the software's lifetime gets shortened to that of this hardware.
|
|
meillo@13
|
612 In contrast, software should be easy to port \(en
|
|
meillo@23
|
613 adaptation is the key to success.
|
|
meillo@13
|
614 .PP
|
|
meillo@15
|
615 (2)
|
|
meillo@15
|
616 .I "Portability of data
|
|
meillo@15
|
617 is best achieved by avoiding binary representations
|
|
meillo@13
|
618 to store data, because binary representations differ from machine to machine.
|
|
meillo@23
|
619 Textual representation is favored.
|
|
meillo@45
|
620 Historically, \s-1ASCII\s0 was the charset of choice.
|
|
meillo@45
|
621 For the future, \s-1UTF\s0-8 might be the better choice.
|
|
meillo@13
|
622 Important is that it is a plain text representation in a
|
|
meillo@13
|
623 very common charset encoding.
|
|
meillo@13
|
624 Apart from being able to transfer data between machines,
|
|
meillo@45
|
625 readable data has the great advantage, that humans are able to directly
|
|
meillo@45
|
626 read and edit it with text editors and other tools from the Unix toolchest.
|
|
meillo@47
|
627 .[ [
|
|
meillo@47
|
628 gancarz
|
|
meillo@47
|
629 unix philosophy
|
|
meillo@47
|
630 .], page 56 ff.]
|
|
meillo@13
|
631 .PP
|
|
meillo@15
|
632 (3)
|
|
meillo@15
|
633 A large
|
|
meillo@15
|
634 .I "range of usability
|
|
meillo@23
|
635 ensures good adaptation, and thus good survival.
|
|
meillo@13
|
636 It is a special distinction if a software becomes used in fields of action,
|
|
meillo@13
|
637 the original authors did never imagine.
|
|
meillo@13
|
638 Software that solves problems in a general way will likely be used
|
|
meillo@45
|
639 for many kinds of similar problems.
|
|
meillo@45
|
640 Being too specific limits the range of usability.
|
|
meillo@13
|
641 Requirements change through time, thus use cases change or even vanish.
|
|
meillo@45
|
642 As a good example in this point,
|
|
meillo@13
|
643 Allman identifies flexibility to be one major reason for sendmail's success:
|
|
meillo@13
|
644 .[
|
|
meillo@44
|
645 allman
|
|
meillo@44
|
646 sendmail
|
|
meillo@13
|
647 .]
|
|
meillo@13
|
648 .QP
|
|
meillo@13
|
649 Second, I limited myself to the routing function [...].
|
|
meillo@13
|
650 This was a departure from the dominant thought of the time, [...].
|
|
meillo@13
|
651 .QP
|
|
meillo@45
|
652 Third, the sendmail configuration file was flexible enough to adapt
|
|
meillo@13
|
653 to a rapidly changing world [...].
|
|
meillo@12
|
654 .LP
|
|
meillo@45
|
655 Successful software adapts itself to the changing world.
|
|
meillo@13
|
656 .PP
|
|
meillo@15
|
657 (4)
|
|
meillo@15
|
658 .I "Reuse of parts
|
|
meillo@15
|
659 is even one step further.
|
|
meillo@13
|
660 A software may completely lose its field of action,
|
|
meillo@13
|
661 but parts of which the software is build may be general and independent enough
|
|
meillo@13
|
662 to survive this death.
|
|
meillo@13
|
663 If software is build by combining small independent programs,
|
|
meillo@45
|
664 then these parts are readily available for reuse.
|
|
meillo@13
|
665 Who cares if the large program is a failure,
|
|
meillo@13
|
666 but parts of it become successful instead?
|
|
meillo@10
|
667
|
|
meillo@48
|
668 .H 2 "Summary
|
|
meillo@0
|
669 .LP
|
|
meillo@45
|
670 This chapter explained central ideas of the Unix Philosophy.
|
|
meillo@45
|
671 For each of the ideas, the advantages they introduce were explained.
|
|
meillo@45
|
672 The Unix Philosophy are guidelines that help to write more valuable software.
|
|
meillo@14
|
673 From the view point of a software developer or software designer,
|
|
meillo@14
|
674 the Unix Philosophy provides answers to many software design problem.
|
|
meillo@14
|
675 .PP
|
|
meillo@14
|
676 The various ideas of the Unix Philosophy are very interweaved
|
|
meillo@14
|
677 and can hardly be applied independently.
|
|
meillo@14
|
678 However, the probably most important messages are:
|
|
meillo@45
|
679 .I "``Keep it simple!''" ,
|
|
meillo@14
|
680 .I "``Do one thing well!''" ,
|
|
meillo@14
|
681 and
|
|
meillo@14
|
682 .I "``Use software leverage!''
|
|
meillo@0
|
683
|
|
meillo@8
|
684
|
|
meillo@8
|
685
|
|
meillo@48
|
686 .H 1 "Case study: \s-1MH\s0
|
|
meillo@18
|
687 .LP
|
|
meillo@30
|
688 The previous chapter introduced and explained the Unix Philosophy
|
|
meillo@18
|
689 from a general point of view.
|
|
meillo@30
|
690 The driving force were the guidelines; references to
|
|
meillo@18
|
691 existing software were given only sparsely.
|
|
meillo@18
|
692 In this and the next chapter, concrete software will be
|
|
meillo@18
|
693 the driving force in the discussion.
|
|
meillo@18
|
694 .PP
|
|
meillo@23
|
695 This first case study is about the mail user agents (\s-1MUA\s0)
|
|
meillo@23
|
696 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP
|
|
meillo@23
|
697 (``new mail handler'').
|
|
meillo@47
|
698 .[
|
|
meillo@47
|
699 nmh website
|
|
meillo@47
|
700 .]
|
|
meillo@23
|
701 \s-1MUA\s0s provide functions to read, compose, and organize mail,
|
|
meillo@45
|
702 but (ideally) not to transfer it.
|
|
meillo@45
|
703 In this document, the name \s-1MH\s0 will be used to include nmh.
|
|
meillo@19
|
704 A distinction will only be made if differences between
|
|
meillo@45
|
705 \s-1MH\s0 and nmh are described.
|
|
meillo@18
|
706
|
|
meillo@0
|
707
|
|
meillo@48
|
708 .H 2 "Historical background
|
|
meillo@0
|
709 .LP
|
|
meillo@19
|
710 Electronic mail was available in Unix very early.
|
|
meillo@30
|
711 The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
|
|
meillo@30
|
712 which was already present in the First Edition.
|
|
meillo@46
|
713 .[ [
|
|
meillo@44
|
714 salus
|
|
meillo@44
|
715 quarter century of unix
|
|
meillo@46
|
716 .], page 41 f.]
|
|
meillo@45
|
717 It was a small program that either printed the user's mailbox file
|
|
meillo@45
|
718 or appended text to someone elses mailbox file,
|
|
meillo@19
|
719 depending on the command line arguments.
|
|
meillo@19
|
720 .[
|
|
meillo@44
|
721 manual mail(1)
|
|
meillo@19
|
722 .]
|
|
meillo@19
|
723 It was a program that did one job well.
|
|
meillo@23
|
724 This job was emailing, which was very simple then.
|
|
meillo@19
|
725 .PP
|
|
meillo@23
|
726 Later, emailing became more powerful, and thus more complex.
|
|
meillo@19
|
727 The simple \f(CWmail\fP, which knew nothing of subjects,
|
|
meillo@19
|
728 independent handling of single messages,
|
|
meillo@45
|
729 and long-time email storage, was not powerful enough anymore.
|
|
meillo@45
|
730 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M')
|
|
meillo@45
|
731 to provide additional functions for emailing.
|
|
meillo@19
|
732 Mail was still one program, but now it was large and did
|
|
meillo@19
|
733 several jobs.
|
|
meillo@23
|
734 Its user interface is modeled after the one of \fIed\fP.
|
|
meillo@19
|
735 It is designed for humans, but is still scriptable.
|
|
meillo@23
|
736 \fImailx\fP is the adaptation of Berkeley Mail into System V.
|
|
meillo@19
|
737 .[
|
|
meillo@44
|
738 ritter
|
|
meillo@44
|
739 mailx history
|
|
meillo@19
|
740 .]
|
|
meillo@30
|
741 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s
|
|
meillo@19
|
742 followed Mail's direction.
|
|
meillo@19
|
743 They are large, monolithic programs which include all emailing functions.
|
|
meillo@19
|
744 .PP
|
|
meillo@23
|
745 A different way was taken by the people of \s-1RAND\s0 Corporation.
|
|
meillo@38
|
746 In the beginning, they also had used a monolithic mail system,
|
|
meillo@30
|
747 called \s-1MS\s0 (for ``mail system'').
|
|
meillo@19
|
748 But in 1977, Stockton Gaines and Norman Shapiro
|
|
meillo@19
|
749 came up with a proposal of a new email system concept \(en
|
|
meillo@45
|
750 one that honored the Unix Philosophy.
|
|
meillo@19
|
751 The concept was implemented by Bruce Borden in 1978 and 1979.
|
|
meillo@19
|
752 This was the birth of \s-1MH\s0 \(en the ``mail handler''.
|
|
meillo@18
|
753 .PP
|
|
meillo@18
|
754 Since then, \s-1RAND\s0, the University of California at Irvine and
|
|
meillo@19
|
755 at Berkeley, and several others have contributed to the software.
|
|
meillo@18
|
756 However, it's core concepts remained the same.
|
|
meillo@23
|
757 In the late 90s, when development of \s-1MH\s0 slowed down,
|
|
meillo@19
|
758 Richard Coleman started with \fInmh\fP, the new mail handler.
|
|
meillo@45
|
759 His goal was to improve \s-1MH\s0 especially in regard of
|
|
meillo@23
|
760 the requirements of modern emailing.
|
|
meillo@19
|
761 Today, nmh is developed by various people on the Internet.
|
|
meillo@18
|
762 .[
|
|
meillo@44
|
763 ware
|
|
meillo@44
|
764 rand history
|
|
meillo@18
|
765 .]
|
|
meillo@18
|
766 .[
|
|
meillo@44
|
767 peek
|
|
meillo@44
|
768 mh
|
|
meillo@18
|
769 .]
|
|
meillo@0
|
770
|
|
meillo@48
|
771 .H 2 "Contrasts to monolithic mail systems
|
|
meillo@0
|
772 .LP
|
|
meillo@19
|
773 All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
|
|
meillo@38
|
774 Although there might actually exist further, very little known,
|
|
meillo@30
|
775 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well.
|
|
meillo@19
|
776 .PP
|
|
meillo@30
|
777 Monolithic \s-1MUA\s0s gather all their functions in one program.
|
|
meillo@30
|
778 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
|
|
meillo@23
|
779 Following is a list of important programs of \s-1MH\s0's toolchest
|
|
meillo@30
|
780 and their function.
|
|
meillo@30
|
781 It gives a feeling of how the toolchest looks like.
|
|
meillo@19
|
782 .IP \(bu
|
|
meillo@19
|
783 .CW inc :
|
|
meillo@30
|
784 incorporate new mail (this is how mail enters the system)
|
|
meillo@19
|
785 .IP \(bu
|
|
meillo@19
|
786 .CW scan :
|
|
meillo@19
|
787 list messages in folder
|
|
meillo@19
|
788 .IP \(bu
|
|
meillo@19
|
789 .CW show :
|
|
meillo@19
|
790 show message
|
|
meillo@19
|
791 .IP \(bu
|
|
meillo@19
|
792 .CW next\fR/\fPprev :
|
|
meillo@19
|
793 show next/previous message
|
|
meillo@19
|
794 .IP \(bu
|
|
meillo@19
|
795 .CW folder :
|
|
meillo@19
|
796 change current folder
|
|
meillo@19
|
797 .IP \(bu
|
|
meillo@19
|
798 .CW refile :
|
|
meillo@45
|
799 refile message into different folder
|
|
meillo@19
|
800 .IP \(bu
|
|
meillo@19
|
801 .CW rmm :
|
|
meillo@19
|
802 remove message
|
|
meillo@19
|
803 .IP \(bu
|
|
meillo@19
|
804 .CW comp :
|
|
meillo@45
|
805 compose new message
|
|
meillo@19
|
806 .IP \(bu
|
|
meillo@19
|
807 .CW repl :
|
|
meillo@45
|
808 reply to message
|
|
meillo@19
|
809 .IP \(bu
|
|
meillo@19
|
810 .CW forw :
|
|
meillo@45
|
811 forward message
|
|
meillo@19
|
812 .IP \(bu
|
|
meillo@19
|
813 .CW send :
|
|
meillo@45
|
814 send prepared message (this is how mail leaves the system)
|
|
meillo@0
|
815 .LP
|
|
meillo@19
|
816 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
|
|
meillo@19
|
817 The user does not leave the shell to run \s-1MH\s0,
|
|
meillo@45
|
818 instead he uses the various \s-1MH\s0 programs within the shell.
|
|
meillo@23
|
819 Using a monolithic program with a captive user interface
|
|
meillo@23
|
820 means ``entering'' the program, using it, and ``exiting'' the program.
|
|
meillo@23
|
821 Using toolchests like \s-1MH\s0 means running programs,
|
|
meillo@45
|
822 alone or in combination with others, also from other toolchests,
|
|
meillo@23
|
823 without leaving the shell.
|
|
meillo@30
|
824
|
|
meillo@48
|
825 .H 2 "Data storage
|
|
meillo@30
|
826 .LP
|
|
meillo@34
|
827 \s-1MH\s0's mail storage is a directory tree under the user's
|
|
meillo@34
|
828 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
|
|
meillo@34
|
829 where mail folders are directories and mail messages are text files
|
|
meillo@34
|
830 within them.
|
|
meillo@34
|
831 Each mail folder contains a file \f(CW.mh_sequences\fP which lists
|
|
meillo@45
|
832 the public message sequences of that folder,
|
|
meillo@45
|
833 for instance the \fIunseen\fP sequence for new messages.
|
|
meillo@34
|
834 Mail messages are text files located in a mail folder.
|
|
meillo@34
|
835 The files contain the messages as they were received.
|
|
meillo@45
|
836 They are named by ascending numbers in each folder.
|
|
meillo@19
|
837 .PP
|
|
meillo@30
|
838 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
|
|
meillo@30
|
839 Alternatives are \fImbox\fP and \fImaildir\fP.
|
|
meillo@30
|
840 In the mbox format all messages are stored within one file.
|
|
meillo@30
|
841 This was a good solution in the early days, when messages
|
|
meillo@30
|
842 were only a few lines of text and were deleted soon.
|
|
meillo@30
|
843 Today, when single messages often include several megabytes
|
|
meillo@30
|
844 of attachments, it is a bad solution.
|
|
meillo@30
|
845 Another disadvantage of the mbox format is that it is
|
|
meillo@30
|
846 more difficult to write tools that work on mail messages,
|
|
meillo@30
|
847 because it is always necessary to first find and extract
|
|
meillo@30
|
848 the relevant message in the mbox file.
|
|
meillo@45
|
849 With the \s-1MH\s0 mailbox format, each message is a separate file.
|
|
meillo@30
|
850 Also, the problem of concurrent access to one mailbox is
|
|
meillo@30
|
851 reduced to the problem of concurrent access to one message.
|
|
meillo@45
|
852 The maildir format is generally similar to the \s-1MH\s0 format,
|
|
meillo@30
|
853 but modified towards guaranteed reliability.
|
|
meillo@30
|
854 This involves some complexity, unfortunately.
|
|
meillo@34
|
855 .PP
|
|
meillo@34
|
856 Working with \s-1MH\s0's toolchest on mailboxes is much like
|
|
meillo@34
|
857 working with Unix' toolchest on directory trees:
|
|
meillo@34
|
858 \f(CWscan\fP is like \f(CWls\fP,
|
|
meillo@34
|
859 \f(CWshow\fP is like \f(CWcat\fP,
|
|
meillo@34
|
860 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
|
|
meillo@34
|
861 \f(CWrefile\fP is like \f(CWmv\fP,
|
|
meillo@34
|
862 and \f(CWrmm\fP is like \f(CWrm\fP.
|
|
meillo@34
|
863 .PP
|
|
meillo@45
|
864 \s-1MH\s0 extends the context of processes in Unix by two more items,
|
|
meillo@45
|
865 for its tools:
|
|
meillo@34
|
866 .IP \(bu
|
|
meillo@34
|
867 The current mail folder, which is similar to the current working directory.
|
|
meillo@34
|
868 For mail folders, \f(CWfolder\fP provides the corresponding functionality
|
|
meillo@34
|
869 of \f(CWcd\fP and \f(CWpwd\fP for directories.
|
|
meillo@34
|
870 .IP \(bu
|
|
meillo@34
|
871 Sequences, which are named sets of messages in a mail folder.
|
|
meillo@34
|
872 The current message, relative to a mail folder, is a special sequence.
|
|
meillo@34
|
873 It enables commands like \f(CWnext\fP and \f(CWprev\fP.
|
|
meillo@34
|
874 .LP
|
|
meillo@45
|
875 In contrast to Unix' context, which is maintained by the kernel,
|
|
meillo@45
|
876 \s-1MH\s0's context must be maintained by the tools themselves.
|
|
meillo@45
|
877 Usually there is one context per user, which resides in his
|
|
meillo@45
|
878 \f(CWcontext\fP file in the \s-1MH\s0 directory,
|
|
meillo@45
|
879 but a user can have several contexts, too.
|
|
meillo@45
|
880 Public sequences are an exception, as they belong to a mail folder,
|
|
meillo@45
|
881 and reside in the \f(CW.mh_sequences\fP file there.
|
|
meillo@34
|
882 .[
|
|
meillo@44
|
883 man page mh-profile mh-sequence
|
|
meillo@34
|
884 .]
|
|
meillo@20
|
885
|
|
meillo@48
|
886 .H 2 "Discussion of the design
|
|
meillo@0
|
887 .LP
|
|
meillo@45
|
888 This section discusses \s-1MH\s0 in regard to the tenets
|
|
meillo@45
|
889 of the Unix Philosophy that Gancarz identified.
|
|
meillo@20
|
890
|
|
meillo@20
|
891 .PP
|
|
meillo@33
|
892 .B "Small is beautiful
|
|
meillo@20
|
893 and
|
|
meillo@33
|
894 .B "do one thing well
|
|
meillo@20
|
895 are two design goals that are directly visible in \s-1MH\s0.
|
|
meillo@45
|
896 Gancarz actually presents \s-1MH\s0 in his book as example under the
|
|
meillo@45
|
897 headline ``Making \s-1UNIX\s0 Do One Thing Well'':
|
|
meillo@46
|
898 .[ [
|
|
meillo@44
|
899 gancarz
|
|
meillo@44
|
900 unix philosophy
|
|
meillo@46
|
901 .], page 125 ff.]
|
|
meillo@20
|
902 .QP
|
|
meillo@20
|
903 [\s-1MH\s0] consists of a series of programs which
|
|
meillo@20
|
904 when combined give the user an enormous ability
|
|
meillo@20
|
905 to manipulate electronic mail messages.
|
|
meillo@20
|
906 A complex application, it shows that not only is it
|
|
meillo@20
|
907 possible to build large applications from smaller
|
|
meillo@20
|
908 components, but also that such designs are actually preferable.
|
|
meillo@20
|
909 .LP
|
|
meillo@45
|
910 The various programs of \s-1MH\s0 were relatively easy to write,
|
|
meillo@45
|
911 because each of them is small, limited to one function,
|
|
meillo@23
|
912 and has clear boundaries.
|
|
meillo@20
|
913 For the same reasons, they are also good to maintain.
|
|
meillo@20
|
914 Further more, the system can easily get extended.
|
|
meillo@20
|
915 One only needs to put a new program into the toolchest.
|
|
meillo@23
|
916 This was done, for instance, when \s-1MIME\s0 support was added
|
|
meillo@20
|
917 (e.g. \f(CWmhbuild\fP).
|
|
meillo@20
|
918 Also, different programs can exist to do the basically same job
|
|
meillo@20
|
919 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
|
|
meillo@45
|
920 .PP
|
|
meillo@20
|
921 If someone needs a mail system with some additionally
|
|
meillo@45
|
922 functions that are not available anywhere yet, he best expands a
|
|
meillo@45
|
923 toolchest system like \s-1MH\s0.
|
|
meillo@45
|
924 There he can add new functionality by simply adding additional
|
|
meillo@45
|
925 programs to the toolchest.
|
|
meillo@45
|
926 There he does not risk to break existing functionality by doing so.
|
|
meillo@20
|
927
|
|
meillo@20
|
928 .PP
|
|
meillo@34
|
929 .B "Store data in flat text files
|
|
meillo@34
|
930 is followed by \s-1MH\s0.
|
|
meillo@34
|
931 This is not surprising, because email messages are already plain text.
|
|
meillo@34
|
932 \s-1MH\s0 stores the messages as it receives them,
|
|
meillo@45
|
933 thus any other tool that works on \s-1RFC\s0\|2822 mail messages can operate
|
|
meillo@34
|
934 on the messages in an \s-1MH\s0 mailbox.
|
|
meillo@45
|
935 All other files \s-1MH\s0 uses are plain text, too.
|
|
meillo@34
|
936 It is therefore possible and encouraged to use the text processing
|
|
meillo@34
|
937 tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
|
|
meillo@20
|
938
|
|
meillo@20
|
939 .PP
|
|
meillo@33
|
940 .B "Avoid captive user interfaces" .
|
|
meillo@19
|
941 \s-1MH\s0 is perfectly suited for non-interactive use.
|
|
meillo@19
|
942 It offers all functions directly and without captive user interfaces.
|
|
meillo@30
|
943 If, nonetheless, users want a graphical user interface,
|
|
meillo@45
|
944 they can have it with \fIxmh\fP or \fIexmh\fP.
|
|
meillo@19
|
945 These are graphical frontends for the \s-1MH\s0 toolchest.
|
|
meillo@19
|
946 This means, all email-related work is still done by \s-1MH\s0 tools,
|
|
meillo@45
|
947 but the frontend calls the appropriate commands when the user
|
|
meillo@30
|
948 clicks on buttons.
|
|
meillo@45
|
949 .PP
|
|
meillo@20
|
950 Providing easy-to-use user interfaces in form of frontends is a good
|
|
meillo@19
|
951 approach, because it does not limit the power of the backend itself.
|
|
meillo@20
|
952 The frontend will anyway only be able to make a subset of the
|
|
meillo@23
|
953 backend's power and flexibility available to the user.
|
|
meillo@20
|
954 But if it is a separate program,
|
|
meillo@20
|
955 then the missing parts can still be accessed at the backend directly.
|
|
meillo@19
|
956 If it is integrated, then this will hardly be possible.
|
|
meillo@45
|
957 An additional advantage is the possibility to have different frontends
|
|
meillo@45
|
958 to the same backend.
|
|
meillo@19
|
959
|
|
meillo@19
|
960 .PP
|
|
meillo@33
|
961 .B "Choose portability over efficiency
|
|
meillo@20
|
962 and
|
|
meillo@33
|
963 .B "use shell scripts to increase leverage and portability" .
|
|
meillo@20
|
964 These two tenets are indirectly, but nicely, demonstrated by
|
|
meillo@30
|
965 Bolsky and Korn in their book about the Korn Shell.
|
|
meillo@20
|
966 .[
|
|
meillo@44
|
967 bolsky korn
|
|
meillo@44
|
968 korn shell
|
|
meillo@20
|
969 .]
|
|
meillo@45
|
970 Chapter\|18 of the book shows a basic implementation
|
|
meillo@20
|
971 of a subset of \s-1MH\s0 in ksh scripts.
|
|
meillo@45
|
972 Of course, this is just a demonstration, but a brilliant one.
|
|
meillo@20
|
973 It shows how quickly one can implement such a prototype with shell scripts,
|
|
meillo@20
|
974 and how readable they are.
|
|
meillo@20
|
975 The implementation in the scripting language may not be very fast,
|
|
meillo@20
|
976 but it can be fast enough though, and this is all that matters.
|
|
meillo@20
|
977 By having the code in an interpreted language, like the shell,
|
|
meillo@20
|
978 portability becomes a minor issue, if we assume the interpreter
|
|
meillo@20
|
979 to be widespread.
|
|
meillo@45
|
980 .PP
|
|
meillo@20
|
981 This demonstration also shows how easy it is to create single programs
|
|
meillo@20
|
982 of a toolchest software.
|
|
meillo@45
|
983 Eight tools (two of them have multiple names) and 16 functions
|
|
meillo@45
|
984 with supporting code are presented to the reader.
|
|
meillo@45
|
985 The tools comprise less than 40 lines of ksh each,
|
|
meillo@30
|
986 in total about 200 lines.
|
|
meillo@45
|
987 The functions comprise less than 80 lines of ksh each,
|
|
meillo@30
|
988 in total about 450 lines.
|
|
meillo@20
|
989 Such small software is easy to write, easy to understand,
|
|
meillo@20
|
990 and thus easy to maintain.
|
|
meillo@23
|
991 A toolchest improves the possibility to only write some parts
|
|
meillo@20
|
992 and though create a working result.
|
|
meillo@45
|
993 Expanding the toolchest, even without global changes,
|
|
meillo@45
|
994 will likely be possible.
|
|
meillo@20
|
995
|
|
meillo@20
|
996 .PP
|
|
meillo@33
|
997 .B "Use software leverage to your advantage
|
|
meillo@20
|
998 and the lesser tenet
|
|
meillo@33
|
999 .B "allow the user to tailor the environment
|
|
meillo@20
|
1000 are ideally followed in the design of \s-1MH\s0.
|
|
meillo@21
|
1001 Tailoring the environment is heavily encouraged by the ability to
|
|
meillo@30
|
1002 directly define default options to programs.
|
|
meillo@30
|
1003 It is even possible to define different default options
|
|
meillo@45
|
1004 depending on the name under which a program is called.
|
|
meillo@45
|
1005 Software leverage is heavily encouraged by the ease of
|
|
meillo@45
|
1006 creating shell scripts that run a specific command line,
|
|
meillo@30
|
1007 built of several \s-1MH\s0 programs.
|
|
meillo@21
|
1008 There is few software that so much wants users to tailor their
|
|
meillo@21
|
1009 environment and to leverage the use of the software, like \s-1MH\s0.
|
|
meillo@45
|
1010 .PP
|
|
meillo@21
|
1011 Just to make one example:
|
|
meillo@23
|
1012 One might prefer a different listing format for the \f(CWscan\fP
|
|
meillo@21
|
1013 program.
|
|
meillo@30
|
1014 It is possible to take one of the distributed format files
|
|
meillo@21
|
1015 or to write one yourself.
|
|
meillo@21
|
1016 To use the format as default for \f(CWscan\fP, a single line,
|
|
meillo@21
|
1017 reading
|
|
meillo@21
|
1018 .DS
|
|
meillo@21
|
1019 scan: -form FORMATFILE
|
|
meillo@21
|
1020 .DE
|
|
meillo@21
|
1021 must be added to \f(CW.mh_profile\fP.
|
|
meillo@21
|
1022 If one wants this different format as an additional command,
|
|
meillo@23
|
1023 instead of changing the default, he needs to create a link to
|
|
meillo@23
|
1024 \f(CWscan\fP, for instance titled \f(CWscan2\fP.
|
|
meillo@21
|
1025 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
|
|
meillo@45
|
1026 as the option should only be in effect for a program that is called as
|
|
meillo@21
|
1027 \f(CWscan2\fP.
|
|
meillo@20
|
1028
|
|
meillo@20
|
1029 .PP
|
|
meillo@33
|
1030 .B "Make every program a filter
|
|
meillo@21
|
1031 is hard to find in \s-1MH\s0.
|
|
meillo@21
|
1032 The reason therefore is that most of \s-1MH\s0's tools provide
|
|
meillo@45
|
1033 basic file system operations for mailboxes.
|
|
meillo@45
|
1034 It is the same reason because of which \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP,
|
|
meillo@45
|
1035 and \f(CWrm\fP aren't filters neither.
|
|
meillo@23
|
1036 \s-1MH\s0 does not provide many filters itself, but it is a basis
|
|
meillo@23
|
1037 to write filters for.
|
|
meillo@45
|
1038 An example would be a mail text highlighter,
|
|
meillo@30
|
1039 that means a program that makes use of a color terminal to display
|
|
meillo@30
|
1040 header lines, quotations, and signatures in distinct colors.
|
|
meillo@45
|
1041 The author's version of such a program is an awk script with 25 lines.
|
|
meillo@21
|
1042
|
|
meillo@21
|
1043 .PP
|
|
meillo@33
|
1044 .B "Build a prototype as soon as possible
|
|
meillo@21
|
1045 was again well followed by \s-1MH\s0.
|
|
meillo@21
|
1046 This tenet, of course, focuses on early development, which is
|
|
meillo@21
|
1047 long time ago for \s-1MH\s0.
|
|
meillo@21
|
1048 But without following this guideline at the very beginning,
|
|
meillo@23
|
1049 Bruce Borden may have not convinced the management of \s-1RAND\s0
|
|
meillo@23
|
1050 to ever create \s-1MH\s0.
|
|
meillo@23
|
1051 In Bruce' own words:
|
|
meillo@46
|
1052 .[ [
|
|
meillo@44
|
1053 ware rand history
|
|
meillo@46
|
1054 .], page 132]
|
|
meillo@21
|
1055 .QP
|
|
meillo@45
|
1056 [...] but [Stockton Gaines and Norm Shapiro] were not able
|
|
meillo@23
|
1057 to convince anyone that such a system would be fast enough to be usable.
|
|
meillo@21
|
1058 I proposed a very short project to prove the basic concepts,
|
|
meillo@21
|
1059 and my management agreed.
|
|
meillo@21
|
1060 Looking back, I realize that I had been very lucky with my first design.
|
|
meillo@21
|
1061 Without nearly enough design work,
|
|
meillo@21
|
1062 I built a working environment and some header files
|
|
meillo@21
|
1063 with key structures and wrote the first few \s-1MH\s0 commands:
|
|
meillo@21
|
1064 inc, show/next/prev, and comp.
|
|
meillo@21
|
1065 [...]
|
|
meillo@21
|
1066 With these three, I was able to convince people that the structure was viable.
|
|
meillo@21
|
1067 This took about three weeks.
|
|
meillo@0
|
1068
|
|
meillo@48
|
1069 .H 2 "Problems
|
|
meillo@0
|
1070 .LP
|
|
meillo@45
|
1071 \s-1MH\s0 is not without problems.
|
|
meillo@30
|
1072 There are two main problems: one is technical, the other is about human behavior.
|
|
meillo@22
|
1073 .PP
|
|
meillo@22
|
1074 \s-1MH\s0 is old and email today is very different to email in the time
|
|
meillo@22
|
1075 when \s-1MH\s0 was designed.
|
|
meillo@45
|
1076 \s-1MH\s0 adapted to the changes pretty well, but it is limited, though.
|
|
meillo@22
|
1077 \s-1MIME\s0 support and support for different character encodings
|
|
meillo@22
|
1078 is available, but only on a moderate level.
|
|
meillo@45
|
1079 This comes from limited development resources.
|
|
meillo@45
|
1080 More active developers could quickly change this.
|
|
meillo@45
|
1081 But \s-1MH\s0 is also limited by design, which is the larger problem.
|
|
meillo@22
|
1082 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend.
|
|
meillo@22
|
1083 These design conflicts are not easily solvable.
|
|
meillo@22
|
1084 Possibly, they require a redesign.
|
|
meillo@45
|
1085 \s-1IMAP\s0 may be too different to the classic mail model,
|
|
meillo@45
|
1086 which \s-1MH\s0 covers, so that \s-1MH\s0 may never support it well.
|
|
meillo@22
|
1087 .PP
|
|
meillo@45
|
1088 The other kind of problem are human habits.
|
|
meillo@45
|
1089 In this world, where almost all \s-1MUA\s0s are monolithic,
|
|
meillo@22
|
1090 it is very difficult to convince people to use a toolbox style \s-1MUA\s0
|
|
meillo@22
|
1091 like \s-1MH\s0.
|
|
meillo@45
|
1092 The habits are so strong, that even people who understand the concept
|
|
meillo@30
|
1093 and advantages of \s-1MH\s0 do not like to switch,
|
|
meillo@30
|
1094 simply because \s-1MH\s0 is different.
|
|
meillo@30
|
1095 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel,
|
|
meillo@45
|
1096 are quite outdated and thus not very appealing, compared to the modern interfaces
|
|
meillo@45
|
1097 of many monolithic \s-1MUA\s0s.
|
|
meillo@20
|
1098
|
|
meillo@48
|
1099 NH 2 "Summary \s-1MH\s0
|
|
meillo@20
|
1100 .LP
|
|
meillo@45
|
1101 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design.
|
|
meillo@31
|
1102 It consists of a toolchest of small tools, each of them does one job well.
|
|
meillo@31
|
1103 The toolchest approach offers great flexibility to the user.
|
|
meillo@45
|
1104 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0.
|
|
meillo@31
|
1105 This makes \s-1MH\s0 a very powerful mail system.
|
|
meillo@45
|
1106 Extending and customizing \s-1MH\s0 is easy and encouraged.
|
|
meillo@31
|
1107 .PP
|
|
meillo@31
|
1108 Apart from the user's perspective, \s-1MH\s0 is development-friendly.
|
|
meillo@31
|
1109 Its overall design follows clear rules.
|
|
meillo@31
|
1110 The single tools do only one job, thus they are easy to understand,
|
|
meillo@31
|
1111 easy to write, and good to maintain.
|
|
meillo@31
|
1112 They are all independent and do not interfere with the others.
|
|
meillo@31
|
1113 Automated testing of their function is a straight forward task.
|
|
meillo@31
|
1114 .PP
|
|
meillo@31
|
1115 It is sad, that \s-1MH\s0's differentness is its largest problem,
|
|
meillo@31
|
1116 as its differentness is also its largest advantage.
|
|
meillo@31
|
1117 Unfortunately, for most people their habits are stronger
|
|
meillo@31
|
1118 than the attraction of the clear design and the power, \s-1MH\s0 offers.
|
|
meillo@0
|
1119
|
|
meillo@8
|
1120
|
|
meillo@8
|
1121
|
|
meillo@48
|
1122 .H 1 "Case study: uzbl
|
|
meillo@32
|
1123 .LP
|
|
meillo@32
|
1124 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0,
|
|
meillo@45
|
1125 which is an old and established software.
|
|
meillo@45
|
1126 This chapter covers uzbl, a fresh new project.
|
|
meillo@45
|
1127 Uzbl is a web browser that adheres to the Unix Philosophy.
|
|
meillo@45
|
1128 Its name comes from the \fILolspeak\fP word for ``usable'';
|
|
meillo@45
|
1129 it is pronounced identical.
|
|
meillo@0
|
1130
|
|
meillo@48
|
1131 .H 2 "Historical background
|
|
meillo@0
|
1132 .LP
|
|
meillo@32
|
1133 Uzbl was started by Dieter Plaetinck in April 2009.
|
|
meillo@44
|
1134 The idea was born in a thread in the Arch Linux Forums.
|
|
meillo@32
|
1135 .[
|
|
meillo@44
|
1136 arch linux forums
|
|
meillo@44
|
1137 browser
|
|
meillo@32
|
1138 .]
|
|
meillo@32
|
1139 After some discussion about failures of well known web browsers,
|
|
meillo@32
|
1140 Plaetinck (alias Dieter@be) came up with a very sketchy proposal
|
|
meillo@32
|
1141 of how a better web browser could look like.
|
|
meillo@32
|
1142 To the question of another member, if Plaetinck would write that program,
|
|
meillo@32
|
1143 because it would sound fantastic, Plaetinck replied:
|
|
meillo@32
|
1144 ``Maybe, if I find the time ;-)''.
|
|
meillo@32
|
1145 .PP
|
|
meillo@32
|
1146 Fortunately, he found the time.
|
|
meillo@32
|
1147 One day later, the first prototype was out.
|
|
meillo@32
|
1148 One week later, uzbl had an own website.
|
|
meillo@47
|
1149 .[
|
|
meillo@47
|
1150 uzbl website
|
|
meillo@47
|
1151 .]
|
|
meillo@32
|
1152 One month after the first code showed up,
|
|
meillo@47
|
1153 a mailing list was installed to coordinate and discuss further development,
|
|
meillo@47
|
1154 and a wiki was added to store documentation and scripts that showed up on the
|
|
meillo@32
|
1155 mailing list and elsewhere.
|
|
meillo@32
|
1156 .PP
|
|
meillo@45
|
1157 In the, now, one year of uzbl's existence, it was heavily developed on various branches.
|
|
meillo@32
|
1158 Plaetinck's task became more and more to only merge the best code from the
|
|
meillo@32
|
1159 different branches into his main branch, and to apply patches.
|
|
meillo@47
|
1160 .[
|
|
meillo@47
|
1161 lwn uzbl
|
|
meillo@47
|
1162 .]
|
|
meillo@32
|
1163 About once a month, Plaetinck released a new version.
|
|
meillo@32
|
1164 In September 2009, he presented several forks of uzbl.
|
|
meillo@47
|
1165 .[ [
|
|
meillo@47
|
1166 uzbl website
|
|
meillo@47
|
1167 .], news archive]
|
|
meillo@38
|
1168 Uzbl, actually, opened the field for a whole family of web browsers with similar shape.
|
|
meillo@32
|
1169 .PP
|
|
meillo@32
|
1170 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl.
|
|
meillo@47
|
1171 .[
|
|
meillo@47
|
1172 lwn uzbl
|
|
meillo@47
|
1173 .]
|
|
meillo@32
|
1174 In September 2009, the uzbl web browser was on \fISlashdot\fP.
|
|
meillo@47
|
1175 .[
|
|
meillo@47
|
1176 slashdot uzbl
|
|
meillo@47
|
1177 .]
|
|
meillo@0
|
1178
|
|
meillo@48
|
1179 .H 2 "Contrasts to other web browsers
|
|
meillo@0
|
1180 .LP
|
|
meillo@32
|
1181 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
|
|
meillo@32
|
1182 most web browsers are monolithic, but uzbl is a frontend to a toolchest.
|
|
meillo@32
|
1183 .PP
|
|
meillo@32
|
1184 Today, uzbl is divided into uzbl-core and uzbl-browser.
|
|
meillo@32
|
1185 Uzbl-core is, how its name already indicates, the core of uzbl.
|
|
meillo@32
|
1186 It handles commands and events to interface other programs,
|
|
meillo@45
|
1187 and also displays webpages by using \fIwebkit\fP as render engine.
|
|
meillo@32
|
1188 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar,
|
|
meillo@32
|
1189 an event manager, yanking, pasting, page searching, zooming, and more stuff,
|
|
meillo@32
|
1190 to form a ``complete'' web browser.
|
|
meillo@32
|
1191 In the following text, the term ``uzbl'' usually stands for uzbl-browser,
|
|
meillo@32
|
1192 so uzbl-core is included.
|
|
meillo@32
|
1193 .PP
|
|
meillo@32
|
1194 Unlike most other web browsers, uzbl is mainly the mediator between the
|
|
meillo@45
|
1195 various tools that cover single jobs.
|
|
meillo@35
|
1196 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket,
|
|
meillo@35
|
1197 and on stdin, and it writes events to a Unix socket and to stdout.
|
|
meillo@35
|
1198 Loading a webpage in a running uzbl instance requires only:
|
|
meillo@32
|
1199 .DS
|
|
meillo@32
|
1200 echo 'uri http://example.org' >/path/to/uzbl-fifo
|
|
meillo@32
|
1201 .DE
|
|
meillo@45
|
1202 The graphical rendering of the webpage is done by webkit,
|
|
meillo@45
|
1203 a web content engine.
|
|
meillo@45
|
1204 Uzbl-core is built around libwebkit.
|
|
meillo@32
|
1205 .PP
|
|
meillo@45
|
1206 Downloads, browsing history, bookmarks, and the like are not provided
|
|
meillo@45
|
1207 by the core itself, like they are in other web browsers.
|
|
meillo@35
|
1208 Uzbl-browser also only provides, so called, handler scripts that wrap
|
|
meillo@35
|
1209 external applications which provide the actual functionality.
|
|
meillo@32
|
1210 For instance, \fIwget\fP is used to download files and uzbl-browser
|
|
meillo@32
|
1211 includes a script that calls wget with appropriate options in
|
|
meillo@32
|
1212 a prepared environment.
|
|
meillo@32
|
1213 .PP
|
|
meillo@32
|
1214 Modern web browsers are proud to have addons, plugins, and modules, instead.
|
|
meillo@32
|
1215 This is their effort to achieve similar goals.
|
|
meillo@35
|
1216 But instead of using existing, external programs, modern web browsers
|
|
meillo@45
|
1217 include these functions.
|
|
meillo@0
|
1218
|
|
meillo@48
|
1219 .H 2 "Discussion of the design
|
|
meillo@0
|
1220 .LP
|
|
meillo@32
|
1221 This section discusses uzbl in regard of the Unix Philosophy,
|
|
meillo@32
|
1222 as identified by Gancarz.
|
|
meillo@32
|
1223
|
|
meillo@32
|
1224 .PP
|
|
meillo@35
|
1225 .B "Make each program do one thing well" .
|
|
meillo@35
|
1226 Uzbl tries to be a web browser and nothing else.
|
|
meillo@36
|
1227 The common definition of a web browser is, of course, highly influenced by
|
|
meillo@36
|
1228 existing implementations of web browsers, although they are degenerated.
|
|
meillo@35
|
1229 Web browsers should be programs to browse the web, and nothing more.
|
|
meillo@45
|
1230 This is the one thing they should do.
|
|
meillo@36
|
1231 .PP
|
|
meillo@45
|
1232 Web browsers should not, for instance, manage downloads.
|
|
meillo@35
|
1233 This is the job download managers exist for.
|
|
meillo@35
|
1234 Download managers do primary care about being good in downloading files.
|
|
meillo@35
|
1235 Modern web browsers provide download management only as a secondary feature.
|
|
meillo@45
|
1236 How could they do this job better, than programs that exist only for
|
|
meillo@35
|
1237 this very job?
|
|
meillo@35
|
1238 And how could anyone want less than the best download manager available?
|
|
meillo@32
|
1239 .PP
|
|
meillo@35
|
1240 A web browser's job is to let the user browse the web.
|
|
meillo@35
|
1241 This means, navigating through websites by following links.
|
|
meillo@36
|
1242 Rendering the \s-1HTML\s0 sources is a different job, too.
|
|
meillo@36
|
1243 It is covered by the webkit render engine, in uzbl's case.
|
|
meillo@35
|
1244 Audio and video content and files like PostScript, \s-1PDF\s0, and the like,
|
|
meillo@36
|
1245 are also not the job of a web browser.
|
|
meillo@36
|
1246 They should be handled by external applications \(en
|
|
meillo@36
|
1247 ones which's job is to handle such data.
|
|
meillo@35
|
1248 Uzbl strives to do it this way.
|
|
meillo@36
|
1249 .PP
|
|
meillo@36
|
1250 Remember Doug McIlroy:
|
|
meillo@35
|
1251 .I
|
|
meillo@35
|
1252 ``Write programs that do one thing and do it well.
|
|
meillo@35
|
1253 Write programs to work together.''
|
|
meillo@35
|
1254 .R
|
|
meillo@35
|
1255 .PP
|
|
meillo@35
|
1256 The lesser tenet
|
|
meillo@35
|
1257 .B "allow the user to tailor the environment
|
|
meillo@35
|
1258 matches good here.
|
|
meillo@35
|
1259 There was the question, how anyone could want anything less than the
|
|
meillo@35
|
1260 best program for the job.
|
|
meillo@45
|
1261 But as personal preferences matter, it is probably more important to ask:
|
|
meillo@35
|
1262 How could anyone want something else than his preferred program for the job?
|
|
meillo@36
|
1263 .PP
|
|
meillo@45
|
1264 Usually users want one program for a specific job.
|
|
meillo@35
|
1265 Hence, whenever the task is, for instance, downloading,
|
|
meillo@45
|
1266 the same download manager should be used.
|
|
meillo@35
|
1267 More advanced users might want to have this download manager in this
|
|
meillo@35
|
1268 situation and that one in that situation.
|
|
meillo@35
|
1269 They should be able to configure it this way.
|
|
meillo@35
|
1270 With uzbl, one can use any download manager the user wants.
|
|
meillo@36
|
1271 To switch to a different one, only one line in a small handler script
|
|
meillo@35
|
1272 needs to be changed.
|
|
meillo@45
|
1273 Alternatively it would be possible to query the program to use by
|
|
meillo@45
|
1274 reading a global file or an environment variable, in the handler script.
|
|
meillo@36
|
1275 .PP
|
|
meillo@45
|
1276 Uzbl does neither have its own download manager nor depends on a
|
|
meillo@45
|
1277 specific one, hence uzbl's browsing abilities will not be lowered by having
|
|
meillo@35
|
1278 a bad download manager.
|
|
meillo@45
|
1279 Uzbl's download capabilities will be just as good as the ones of the best
|
|
meillo@36
|
1280 download manager available on the system.
|
|
meillo@38
|
1281 Of course, this applies to all of the other supplementary tools, too.
|
|
meillo@32
|
1282
|
|
meillo@32
|
1283 .PP
|
|
meillo@36
|
1284 .B "Use software leverage to your advantage" .
|
|
meillo@36
|
1285 Uzbl is designed to be extended by external tools.
|
|
meillo@36
|
1286 These external tools are usually wrapped by small handler shell scripts.
|
|
meillo@36
|
1287 Shell scripts are the glue in this approach.
|
|
meillo@36
|
1288 They make the various parts fit together.
|
|
meillo@36
|
1289 .PP
|
|
meillo@45
|
1290 The history mechanism of uzbl shall be presented as an example.
|
|
meillo@36
|
1291 Uzbl is configured to spawn a script to append an entry to the history
|
|
meillo@36
|
1292 whenever the event of a fully loaded page occurs.
|
|
meillo@45
|
1293 The script to append the entry to the history is not much more than:
|
|
meillo@36
|
1294 .DS
|
|
meillo@36
|
1295 #!/bin/sh
|
|
meillo@36
|
1296 file=/path/to/uzbl-history
|
|
meillo@36
|
1297 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file
|
|
meillo@36
|
1298 .DE
|
|
meillo@36
|
1299 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title.
|
|
meillo@45
|
1300 .PP
|
|
meillo@45
|
1301 For loading an entry, a key is bound to spawn a load-from-history script.
|
|
meillo@36
|
1302 The script reverses the history to have newer entries first,
|
|
meillo@45
|
1303 then displays \fIdmenu\fP to let the user select an item,
|
|
meillo@36
|
1304 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe.
|
|
meillo@45
|
1305 With error checking and corner case handling removed,
|
|
meillo@45
|
1306 the script looks like this:
|
|
meillo@36
|
1307 .DS
|
|
meillo@36
|
1308 #!/bin/sh
|
|
meillo@36
|
1309 file=/path/to/uzbl-history
|
|
meillo@36
|
1310 goto=`tac $file | dmenu | cut -d' ' -f 3`
|
|
meillo@36
|
1311 echo "uri $goto" > $4
|
|
meillo@36
|
1312 .DE
|
|
meillo@36
|
1313 \f(CW$4\fP expands to the path of the command input pipe of the current
|
|
meillo@36
|
1314 uzbl instance.
|
|
meillo@32
|
1315
|
|
meillo@32
|
1316 .PP
|
|
meillo@33
|
1317 .B "Avoid captive user interfaces" .
|
|
meillo@36
|
1318 One could say, that uzbl, to a large extend, actually \fIis\fP
|
|
meillo@36
|
1319 a captive user interface.
|
|
meillo@37
|
1320 But the difference to most other web browsers is, that uzbl is only
|
|
meillo@45
|
1321 the captive user interface frontend (and the core of the backend).
|
|
meillo@38
|
1322 Many parts of the backend are independent of uzbl.
|
|
meillo@45
|
1323 Some are distributed with uzbl, for some external programs,
|
|
meillo@45
|
1324 handler scripts are distributed,
|
|
meillo@45
|
1325 but arbitrary additional functionality can be added if desired.
|
|
meillo@37
|
1326 .PP
|
|
meillo@37
|
1327 The frontend is captive \(en that is true.
|
|
meillo@37
|
1328 This is okay for the task of browsing the web, as this task is only relevant
|
|
meillo@37
|
1329 for humans.
|
|
meillo@37
|
1330 Automated programs would \fIcrawl\fP the web.
|
|
meillo@37
|
1331 That means, they read the source directly.
|
|
meillo@37
|
1332 The source includes all the semantics.
|
|
meillo@37
|
1333 The graphical representation is just for humans to transfer the semantics
|
|
meillo@37
|
1334 more intuitively.
|
|
meillo@32
|
1335
|
|
meillo@32
|
1336 .PP
|
|
meillo@33
|
1337 .B "Make every program a filter" .
|
|
meillo@37
|
1338 Graphical web browsers are almost dead ends in the chain of information flow.
|
|
meillo@37
|
1339 Thus it is difficult to see what graphical web browsers should filter.
|
|
meillo@45
|
1340 Graphical web browsers exist almost only to be interactively used by humans.
|
|
meillo@37
|
1341 The only case when one might want to automate the rendering function is
|
|
meillo@37
|
1342 to generate images of rendered webpages.
|
|
meillo@37
|
1343
|
|
meillo@37
|
1344 .PP
|
|
meillo@37
|
1345 .B "Small is beautiful"
|
|
meillo@45
|
1346 is not easy to apply to a web browser, because modern web technology
|
|
meillo@45
|
1347 is very complex, hence the rendering task is very complex.
|
|
meillo@45
|
1348 Modern web browsers have to consist of many thousand lines of code,
|
|
meillo@37
|
1349 unfortunately.
|
|
meillo@37
|
1350 Using the toolchest approach and wrappers can split the browser into
|
|
meillo@37
|
1351 several small parts, tough.
|
|
meillo@37
|
1352 .PP
|
|
meillo@45
|
1353 As of March 2010, uzbl-core consists of about 3\,500 lines of C code.
|
|
meillo@37
|
1354 The distribution includes another 3\,500 lines of Shell and Python code,
|
|
meillo@37
|
1355 which are the handler scripts and plugins like a modal interface.
|
|
meillo@38
|
1356 Further more, uzbl uses functionality of external tools like
|
|
meillo@38
|
1357 \fIwget\fP and \fInetcat\fP.
|
|
meillo@37
|
1358 Up to this point, uzbl looks pretty neat and small.
|
|
meillo@38
|
1359 The ugly part of uzbl is the web content renderer, webkit.
|
|
meillo@37
|
1360 Webkit consists of roughly 400\,000 (!) lines of code.
|
|
meillo@38
|
1361 Unfortunately, small web render engines are not possible anymore
|
|
meillo@38
|
1362 because of the modern web.
|
|
meillo@35
|
1363
|
|
meillo@35
|
1364 .PP
|
|
meillo@35
|
1365 .B "Build a prototype as soon as possible" .
|
|
meillo@35
|
1366 Plaetinck made his code public, right from the beginning.
|
|
meillo@38
|
1367 Discussion and development was, and still is, open to everyone interested.
|
|
meillo@38
|
1368 Development versions of uzbl can be obtained very simply from the code
|
|
meillo@38
|
1369 repository.
|
|
meillo@38
|
1370 Within the first year of uzbl's existence, a new version was released
|
|
meillo@35
|
1371 more often than once a month.
|
|
meillo@38
|
1372 Different forks and branches arose.
|
|
meillo@45
|
1373 They introduced new features, which were tested for suitability
|
|
meillo@45
|
1374 for the main branch.
|
|
meillo@35
|
1375 The experiences of using prototypes influenced further development.
|
|
meillo@35
|
1376 Actually, all development was community driven.
|
|
meillo@38
|
1377 Plaetinck says, three months after uzbl's birth:
|
|
meillo@35
|
1378 ``Right now I hardly code anything myself for Uzbl.
|
|
meillo@35
|
1379 I just merge in other people's code, ponder a lot, and lead the discussions.''
|
|
meillo@35
|
1380 .[
|
|
meillo@44
|
1381 lwn
|
|
meillo@44
|
1382 uzbl
|
|
meillo@35
|
1383 .]
|
|
meillo@32
|
1384
|
|
meillo@0
|
1385
|
|
meillo@48
|
1386 .H 2 "Problems
|
|
meillo@0
|
1387 .LP
|
|
meillo@38
|
1388 Similar to \s-1MH\s0, uzbl, too suffers from being different.
|
|
meillo@38
|
1389 It is sad, but people use what they know.
|
|
meillo@38
|
1390 Fortunately, uzbl's user interface can look and feel very much the
|
|
meillo@38
|
1391 same as the one of the well known web browsers,
|
|
meillo@38
|
1392 hiding the internal differences.
|
|
meillo@38
|
1393 But uzbl has to provide this similar look and feel to be accepted
|
|
meillo@38
|
1394 as a ``normal'' browser by ``normal'' users.
|
|
meillo@37
|
1395 .PP
|
|
meillo@45
|
1396 Though, the more important problem is the modern web.
|
|
meillo@38
|
1397 The modern web is simply broken.
|
|
meillo@38
|
1398 It has state in a state-less protocol,
|
|
meillo@38
|
1399 it misuses technologies,
|
|
meillo@38
|
1400 and it is helplessly overloaded.
|
|
meillo@38
|
1401 The result are web content render engines that must consist
|
|
meillo@38
|
1402 of hundreds of thousands lines of code.
|
|
meillo@38
|
1403 They also must combine and integrate many different technologies,
|
|
meillo@45
|
1404 only to make our modern web accessible.
|
|
meillo@38
|
1405 Website to image converter are hardly possible to run without
|
|
meillo@38
|
1406 human interaction because of state in sessions, impossible
|
|
meillo@38
|
1407 deep-linking, and unautomatable technologies.
|
|
meillo@37
|
1408 .PP
|
|
meillo@38
|
1409 The web was misused to provide all kinds of imaginable wishes.
|
|
meillo@38
|
1410 Now web browsers, and eventually the users, suffer from it.
|
|
meillo@37
|
1411
|
|
meillo@8
|
1412
|
|
meillo@48
|
1413 .H 2 "Summary uzbl
|
|
meillo@32
|
1414 .LP
|
|
meillo@38
|
1415 ``Uzbl is a browser that adheres to the Unix Philosophy'',
|
|
meillo@38
|
1416 that is how uzbl is seen by its authors.
|
|
meillo@38
|
1417 Indeed, uzbl follows the Unix Philosophy in many ways.
|
|
meillo@38
|
1418 It consists of independent parts that work together,
|
|
meillo@45
|
1419 while its core is mainly a mediator which glues the parts together.
|
|
meillo@38
|
1420 .PP
|
|
meillo@38
|
1421 Software leverage can excellently be seen in uzbl.
|
|
meillo@45
|
1422 External tools are used, independent tasks are separated
|
|
meillo@45
|
1423 in independent parts and glued together with small handler scripts.
|
|
meillo@38
|
1424 .PP
|
|
meillo@38
|
1425 As uzbl, more or less, consists of a set of tools and a bit
|
|
meillo@38
|
1426 of glue, anyone can put the parts together and expand it
|
|
meillo@38
|
1427 in any desired way.
|
|
meillo@38
|
1428 Uzbl is very flexible and customizable.
|
|
meillo@38
|
1429 These properties make it valuable for advanced users,
|
|
meillo@38
|
1430 but may keep novice users from using it.
|
|
meillo@38
|
1431 .PP
|
|
meillo@45
|
1432 But uzbl's main problem is the modern web, that makes it hard
|
|
meillo@38
|
1433 to design a sane web browser.
|
|
meillo@38
|
1434 Despite this bad situation, uzbl does a fairly good job.
|
|
meillo@32
|
1435
|
|
meillo@8
|
1436
|
|
meillo@48
|
1437 .H 1 "Final thoughts
|
|
meillo@0
|
1438
|
|
meillo@48
|
1439 .H 2 "Quick summary
|
|
meillo@0
|
1440 .LP
|
|
meillo@0
|
1441 good design
|
|
meillo@0
|
1442 .LP
|
|
meillo@0
|
1443 unix phil
|
|
meillo@0
|
1444 .LP
|
|
meillo@0
|
1445 case studies
|
|
meillo@0
|
1446
|
|
meillo@48
|
1447 .H 2 "Why people should choose
|
|
meillo@0
|
1448 .LP
|
|
meillo@0
|
1449 Make the right choice!
|
|
meillo@0
|
1450
|
|
meillo@47
|
1451
|
|
meillo@47
|
1452 .bp
|
|
meillo@47
|
1453 .TL
|
|
meillo@47
|
1454 References
|
|
meillo@47
|
1455 .LP
|
|
meillo@47
|
1456 .XS
|
|
meillo@47
|
1457 .sp .5v
|
|
meillo@47
|
1458 .B
|
|
meillo@47
|
1459 References
|
|
meillo@47
|
1460 .XE
|
|
meillo@47
|
1461 .ev r
|
|
meillo@0
|
1462 .rm ]<
|
|
meillo@0
|
1463 .de ]<
|
|
meillo@0
|
1464 .LP
|
|
meillo@0
|
1465 .de FP
|
|
meillo@0
|
1466 .IP \\\\$1.
|
|
meillo@0
|
1467 \\..
|
|
meillo@0
|
1468 .rm FS FE
|
|
meillo@0
|
1469 ..
|
|
meillo@42
|
1470 .nr PS -1
|
|
meillo@42
|
1471 .nr VS -1
|
|
meillo@0
|
1472 .[
|
|
meillo@0
|
1473 $LIST$
|
|
meillo@0
|
1474 .]
|
|
meillo@47
|
1475 .nr PS +1
|
|
meillo@47
|
1476 .nr VS +1
|
|
meillo@47
|
1477 .ev
|
|
meillo@47
|
1478
|
|
meillo@42
|
1479 .bp
|
|
meillo@47
|
1480 .TL
|
|
meillo@47
|
1481 Table of Contents
|
|
meillo@47
|
1482 .LP
|
|
meillo@47
|
1483 .PX no
|
